The electronic tagging of criminals to check whether they are indoors at night is costing the taxpayer millions and does nothing to stop reoffending, the probation officers' union has said.

The Home Office says the home detention curfew is successfully reintegrating criminals back into the community. The UK already has the biggest tagging scheme in Europe - and there are plans to double the numbers by 2008.

But offenders told BBC ONE's Real Story (Monday 25 April, 7.30pm, BBC One) how they repeatedly committed crimes while "on the tag" and some parents told the programme that their children would benefit more from a term in prison.

We asked five commentators on crime whether or not electronically monitoring criminals is the right option.

Martin Neary is Chief Executive of the National Offenders Management Service which runs the tagging policy for England and Wales. He is also former Director General of the Prison Service.

While people are on the tag I am entirely convinced that the amount of crime they are committing is reduced.

Reconviction rates are a very crude measure - tagging may not reduce them and we do not claim that it will but I am quite satisfied that people who are tagged are committing much less crime than if we did not have this facility.

There is an important distinction between reconviction rates and reducing crime. We measure reconviction rates in a fairly blunt way. If someone is reconvicted for any crime - a single crime - in a two-year period after being released from custody then we measure that as a reconviction.

But we are tagging a lot of very persistent offenders, many of whom will be offending every day and I am quite satisfied from talking to them, to their probation officers and to their parents that while they are tagged, while they are at home and unable to go out, the amount of crime they get involved in is significantly reduced.

We also lock criminals up. We have fewer people on Home Detention Curfew now than we did last year. We only let people out after a careful risk assessment.

For example, of those who are tagged, only 9% of them re-offend within 6 months. Of those people who are not tagged, 40% of them re-offend. That suggests we are getting the risk assessment about right.

Of all the people released from prison on Home Detention Curfew since it began in 1999, only 3% have been convicted of crime, been cautioned by the police or are awaiting prosecution.

Harry Fletcher is spokesman for the National Association of Probation Officers.

It is essential to remember that there are two schemes here. The first is the Home Detention curfew - which is in effect early release from prison. It is a means of controlling the prison population.

But thousands and thousands of prisoners come out on parole every year and the government could have extended that system without the expense of the tag.

The second scheme is the Freestanding Curfew Order which is a sentence of the court and the community and I believe it is expensive, inefficient and it does not reduce crime.

Back in 1995 when the curfew order first came in, the Home Office issued the following guidance to magistrates and judges as to what electronic monitoring cannot do: a) Stop crime, b) Stop offenders breaching curfew, and c) Stop offenders committing further offences.

So they have known that for 10 years but have continued with this scheme regardless - and there are about 9,000 on the tag at any one time.

Parliamentary questions last year, and correspondence between Mark Oaten, the Lib Dem Home Affairs spokesman, and the Minister Paul Goggins, showed that putting somebody on curfew in the community cost £6,500 over one year, compared with £3,800 with someone on probation. So it's virtually twice as expensive.

And staff over the country have been feeding me examples of breaches: From Gloucester, one man was breached 29 times before he came back to court and another person 34 times.

Staff across the whole of London say that because the system is so inefficient, by the time offenders have got back to court the order is already finished so they tend not to be re-sentenced.

A better way to stop re-offending would be supervision by human beings in the field, whether a probation officer or a social worker, who actively intervene and try to stop the causes of crime. The curfew order does not do that so it is not surprising that the breaching and reoffending rates are so high.

Norman Brennan is from the Victims of Crime Trust. He has also been a serving police officer in London for the past 25 years.

I want to see tagging scrapped - but for reasons different to those of Napo. I think it should go because it compromises the safety of the public and the safety of the community should be paramount.

There are already 12 alternatives to imprisonment - final warnings, cautions, community service, conditional discharge, etc - and this is already too many. The UK's criminal justice system is in crisis. The sentence no longer fits the crime.

Tagging is meant to keep offenders indooors bewteen 7pm and 7am but even if the curfew is obeyed it does not stop those such as drug dealers from committing crime.

The re-offending rate of people on tags is huge. Consider the tragic story of Marian Bates who was shot dead in her jewellery shop by armed raiders, one of whom should have been wearing an electronic tag. She is one of many victims who have suffered crime at the hands of taggees.

The re-offending rate of those put on community service is 77% over two years.

More offenders need to be locked up and more prisoners should be kept in jail for 24 hours until the end of their term.

Karen Doyle works for Derby City Council's Youth Offending Service. She helps to manage the Intensive Supervision and Surveillance Programme (ISSP) which oversees young people who are tagged.

My team works with tagged offenders aged up to 17 and our view is that tagging gives them a chance to be rehabilitated back into the community.

No-one of that age should be put in jail unless they pose a serious risk to the public. They would be going into prison as damaged individuals, usually for a short period of time, and when they came back out they would in any case have to be rehabilitated.

If you lock these kids up for long enough they will get involved with hardened criminals - they will become institutionalised.

An essential part of the ISSP scheme is that it urges the offenders to get some structure and routine in their lives. These are people with complex needs. Often the underlying reasons for their crimes are family disfunction, drug or alcohol problems, homelessness, etc.

They have to meet a stringent criteria to be offered this scheme - for example, they must have been charged, warned or convicted of four or more offences in the last 12 months, or have committed a one-off offence serious enough to warrant custody.

The reason for this is that the ISSP programme offers more supervision and surveillance than any other court order. Our aim is to build education, training or employment into their lives with a minimum of 25 hours of supervision a week. Our cognitive behavioural programme is very in-depth and helps offenders to identify alternative ways of behaving.

The tag helps us to meet our overall aim of helping them to achieve structure because they have to be home by a certain time. This stops the pattern of sleeping during the day and going out at night so they are more likely to get a "normal" lifestyle.

There are many more resources to tackle social exclusion in the community than there are in prison. We are also able to offer a scheme tailored to an individual's cultural needs.

We have an excellent relationship with the police in Derby. They are familiar with our tagged offenders which helps to maximise surveillance.